Constant viscosity method of lining container closures



Sept. 8, 1953 H. E. COOPER ET AL 2,651,586

CONSTANT VISCOSITY METHOD o1 LINING CONTAINER CLOSURES Filed March 1, 1949 Inventors 7 HENRYE. COOPER DUNBARL. .SHA/V/(Ll/V y mam Brwwwe.

Attorney Patented Sept. 8, 1953 CONSTANT VISCOSITY METHOD OF LINlN G CONTAINER CLOSURES Henry E. Cooper, Waltham, and Dunbar L.

Shanklin,

Winchester, Mass.,

assignors to Dewey and Almy Chemical Company, Cambridge, Mass., a corporation of Massachusetts Application March 1, 1949, Serial No. 79,046

Claims. 1

This invention is concerned with a method of lining container closures with paste type lining compositions or compound and incorporates apparatus for lining closures with such compound. Paste type lining compositions are composed of discrete small particles of resin, fillers and a liquid plasticizer. Their characteristic feature is that the resin particles are insoluble in the plasticizer at room temperature, but are completely soluble in the plasticizer at some higher temperature, usually about 300 F. After the resin has dissolved in the plasticizer, a permanent rubbery gel is formed when the mass is cooled.

The operation of applying a liquid compound intended to form the sealing gasket of a metal or glass container and convertifig the band of compound into a solid,'deformable sealing gasket is known as lining. Lining has had a long technological development, but still remains unique in its exacting demands. Astronomical numbers of closures are regularly lined at speeds of over 200 a minute, which means, in manyinstances, that a stripe of compound inches long and of an inch wide has been applied to the closure in about of a second, yet the maximum variation in the weight of the finished gasketsis held commercially to plus or minus 5%. Obviously, a machine which feeds closures from a stack, rotates them on a chuck, lines them by flowing liquid compound around the periphery, and then conveys the lined closures away at these speeds and with such exactness is a precise, closely adjusted mechanism. It is obvious that the compound itself must possess a uniform and constant viscosity to be fed in uniform and precisely controlled quantities. Primarily, it was the development of the art of controlling the viscosity of a liquid lining composition, whether that compound be water base (latex) or asolution in an organic liquid which made the enormous production of container closures possible.

In contrast with the relatively stable viscosities found in older type of sealing compositions, the newly developed paste type compositions exhibit viscosities which vary through enormous ranges with minute changes in temperature. For example, a paste compound now in commercial use exhibits a viscosity of 8500 centipoises at 96 F. At 100 F. the viscosity falls to 3660 centipoises and at 105 F. the viscosity is 1500 centipoises. At 110 F. the viscosity is 900 centipoises. It falls to a minimum of 600 centipoises at 140 F. and. shoots up to 6000 centipoises as the temperature rises to 163 F.

It follows that such a compound cannot flow through an intermittently operating nozzle in such a manner that a constant quantity is repetitively delivered in a unit time, unless at all times the compound is held at constant temperature. But constant temperature alone is not enough. Many (but not all) paste lining compounds are highly thixotropic. If the compound is allowed to assume a state of rest even momentarily, the thixotropic yield value builds up to such limits that the compound cannot again be set in' motion without an excessive pressure I surge.

Many paste compounds are stiff sludgy masses at room.temperature and must be heated, for example, from to 130 F. to reduce them to lining viscosities; but very close to the temperature where they possess minimum viscosity, the resin which hitherto has been insoluble in the plasticizer begins to solvate. Since solvation is progressive, a slight rise in temperature will shoot the viscosity upward to unworkably high limits.

'These extremely sensitive critical viscositytemperature relationships of paste lining compounds make the lining of closures to present day standards of accuracy so difficult as to be commercially impracticable when using conventional apparatus. Repeatedly, in the early developmental stages of this invention, we found that we could not heat the paste lining compound in, for example, a jacketed kettle and bring its mass temperature up to say F. without causing some solvation of the resin and sending the viscosity wildly out of control. Repeatedly, too, when working with thixotropic compounds, we found that wecould not deliver accurately measured quantities of compound to the closure by the normal air pressure method of delivering liquid compound to an intermittently operating lining nozzle because of the false viscosities which built up in the system when the compound came to rest as the valve closed.

From this experience, we reasoned that if an accurate control of viscosity was to be maintained, (1) the mass of compound could not be allowed to assume a state of rest and (2) the correct degree of heat had to be developed within the compound; it should not be transmitted to the compound from some higher temperature level.

The present invention is concerned with the creation and maintenance of a constant viscosity in paste type container sealing compositions. It assures the uniform delivery of a liquified paste composition to the sealing area of the closure.

It delivers an amount of compound which at all times lies within the weight-limit tolerances, and it permits fresh amounts of cold compound to be added as needed without stopping the machine or changing the accuracy of its delivery. Our invention permits the generation of heat within the compound and liberates that heat in direct relationship to the viscosity which the compound exhibits. Additionally it does not permit the high yield values to be established and consequently avoids the pressure surges which thixotropic compounds introduce. In consequence, we achieve the objects of our invention, which are primarily to deliver an exact quantity of a paste compound to the periphery of a container closure in a predetermined short period of time, and incidentally to control both the temperature and the momentary viscosity of the compound within such narrow limits that exact quantities of compound can be delivered. Generally speaking, we repeatedly pass the compound through a closed pipe circuit, keeping it in motion at all times to minimize the effect of thixotropy, and we heat the compound by the mechanical work performed upon it by an overcapacity pump.

I-Ieating the compound internally may be accomplished in numerous ways. We have passed the compound through a high-frequency-di-electric field. Work can be performed on the compound by mechanical or electric oscillators, or pulsing diaphragms can be inserted in the pipe circuit, but by far the simplest mechanism which releases its energy as sensible heat within the compound is a positive displacement pump because at the same time that it heats the compound, it builds up the pressure which is necessary to move the material through the pipe circuit and force a part of the material through the nozzle onto the closure.

Figure 1 is a diagrammatic representation of the apparatus used in the process.

Figure 2 is a top plan view of the compound container.

The system comprises a positive displacement pump Hi, preferably of the gear type, which is driven by a variable ratio drive connected to an electric motor (not shown). The discharge from the pump passes into the discharge conduit H which is connected to an equalizer coil I2. Coil I2 is immersed in the water tank l3. From coil 12 the compound passes through the conduit M to the lining assembly l5 which comprises a lining nozzle IE or the needle valve type and an air chamber [1. Any pulsing flow of the compound caused by the operation of the needle valve nozale #5 is cushioned by a supply of air l8 trapped in the air chamber H. The compound leaves the air chamber I! through the conduit [9 and is discharged through the open end of conduit 19. End 20 of the conduit 19 is located very close to the apex 2! of the conical bottom 22 of the compound supply tank 23. A grid work 24 of crossed small-diameter pipes which extend through the conical base section 22 so that the interior of the pipes is in direct communication with the water contained in tank I3 forms a support for the cold, solid compound which is shoveled or dumped into the tank 23 from time to time. Alternatively, the grid may be heated electrically or by other means, but we prefer the structure shown. The water in tank 13 is maintained at a temperature close to that at which it is intended to line the compound on the closure 25 and in practice, an efiort is made to maintain time operation, or 2 below the lining temperature which is sometimes called for in summer operation. A small pump 26 driven by an electric motor (not shown) maintainsa constant circulation of water within tank 13 through the pipes 2'! and 28.

For the sake of clarity, the electric heating .coils used to raise the water to the required temperature are not shown. The operation of the system is as follows: Assuming that the system was empty at the start of the operation, cold, semi-solid compound is placed inside tank 23 where it occupies the position 29 as shown. As the water temperature rises, the compound is heated by the water flowing through the grid pipes 24 and small pieces and drips of the compound then begin to fall onto the conical base 22 of the compound tank 23. When a sufiicient amount of :material has been melted so that there is no danger of sucking air into the system through the input port 30 which is located at the apex of the cone 2,2, by-pass valve 3| is opened, upper by-pass valve 32, conveniently an adjustable spring-loaded relief valve, is also opened and flow control valve 33 is opened. Pump [I] is then started, and after .it has run a minute or two so that it warms up the .compound in the pump and in its immediate vicinity, valve 31 is closed. The compound is then forced through the conduit 11, through the equalizing coil 32, out through the conduit l4, through the by-pass conduit 34 and Joy-pass valve 32 and back through the continuation of the conduit 19 to join the compound which now is flowing or sliding down the interior wall of the conical base 22. When this compound is warmed nearly to the operating temperature, by-pass valve 32 is closed. The compound is then forced through those portions of the conduits I4 and [9 which connect with the air chamber I1. After a few minutes of operation, to permit the compound in the pipes to reach an equilibrium condition, the lining machine may be started and the unlined closures rotated under the intermittently operated lining nozzle H5.

The amount of compound pumped and circulated is much greater than the amount of compound discharged through nozzle l6. As an ex ample, when lining 63 mm. coffee caps, about /2 pound of compound is applied to 200 .closures which have passed under nozzle 16 in one minute, but approximately 11 pounds of compound have been pumped through the piping circuit at the same time.

The amount of heat supplied to the compound mechanically by the motor driven pump 10 is a substantial amount of that required to raise the temperature to the operating level. The heat supplied from the water is essentially that amount which is sufiicient to compensate for radiation losses and either to melt the compound or to allow the system to start operating or both. The mechanical work transformed to heat with in the compound by the pump it! is a direct function of (1) speed of pumping and (2) back pressure on the system. The heat generated within the compound is caused by the dissipation of mechanical energy in overcoming the internal friction of the compound while it is being pumped through the circuit, and also the friction between the compound and the walls and other parts of the circuit. The throttle valve 33 controls the resistance to flow of the compound and also is a factor in controlling the back pressure on the pump.

Speed is adjusted by the variable drive mechanism. Back pressure is adjusted by the valve 33. With these conditions set,-the system, after coming to equilibrium, is largely self-regulating. For example, if aslug of high viscosity compound enters the pump, more work will be performed on it. Its temperature will rise and its viscosity will fall. If the viscosity falls, less work will appear as heat. Thus the system tends to seek stable operation.

The amount of mechanical energy converted into heat is illustrated below by two commercial compounds: (A) a pasty compound used for forming side seals on container closures and (B) a more fluid compound used for forming top seals on container closures. In both instances the compound dropped off the grid and entered the circulating flow at an average temperature of 80 F.

Physical properties Compound Compound Specific gravity 1.29 l. 68 Specific heat O 21 0. 24 Viscosity at 80 F.:

6 R. M., c. p- 642,000--.- 40,000 Unreadable 42, 300

Circulating system data Compound Compound Back Pressure at Pump ..p. s. i. g" 225 70 Speed of Pump R. P. M 100 100 Volume Pumped lb. per min 8.8 11. 5 Temperature (avg) at Entrance F 80 80 Temperature at Delivery F. 110 102 QuantityDelivered to Closures, lb. per min. 0.66 0. 40 Quantity Delivered as Percent Total Pumped 7.5 3. 5 Heat Required B. t. u. per min 6.1 2.1 Heat Developed Internally by Pumping B. t. u. per mini. 4.6 1. 4 Percentage of heat requirement that is supplied by pump 75 67 These conditions held the weight tolerance limits of linings on closures successfully for long runs.

Notes-Viscosity measurements were determined by the Brookfield Viscosimeter using the number 5 spindle for compound A at shear rates of 6 and 60 R. P. M. The number 3 spindle was used to measure viscosity of compound B at shear rates of 6 and 60 R. P. M.

We claim:

1. The process of lining container closures with controlled uniform amounts of a heated, paste-type lining compound, which is characterized by a large change in viscosity with a small change in temperature, which includes maintaining a large volume of the compound at a substantially uniform viscosity by recirculating the compound through a conduit system by means of a positive displacement pump, adjusting the speed and the delivery pressure of the pump to secure the release of the heat equivalent of the work performed on the compound as sensible heat within the compound in such amount and at such a rate that the compound being circulated is maintained at a substantially uniform elevated temperature, intermittently discharging a minor fraction only of said circulating compound at a substantially uniform rate onto successive container closures and continuously maintaining the volume of compound being circulated by entraining the makeup quantity of compound in the low pressure side of the circulating stream at a point approaching the. inlet side of the pump. I

2. The process of lining container closures as described in claim 1 wherein the makeup quantity of compound entrained in the low pressure side of the circulating stream is preheated to a temperature level lower than the temperature level of the compound in the circulating stream and is broken into small pieces before entering said circulating stream by passing through a heated grid located at the entrance of said makeup quantity of compound into the low pressure side of the circulating stream.

3. The process of lining container closures with controlled uniform amounts of a heated, paste-type lining compound which is characterized by a large reversible decrease in viscosity with a small increase in temperature at temperatures below the solvation temperature of said compound and by a large irreversible increase in viscosity with a small increase of temperature at temperature levels above the solvation temperature of said compound, which includes maintaining a large volume of the compound at a substantially uniform viscosity by recirculating the compound through a conduit system, generating sensible heat within said compound in such amount and at such a rate that the compound being circulated is maintained at a substantially uniform temperature less than the solvation temperature of the compound, intermittently discharging a minor fraction only of said circulating compound at a substantially uniform rate onto successive container closures and continuously maintaining the volume of the compound being circulatedby entraining the makeup quantity of the compound in the low pressure side of the circulating stream at a point approaching the inlet side of the pump.

4. The process of lining container closures with controlled uniform amounts of a heated, pastetype lining compound which is characterized by large changes in viscosity with small changes in temperature, which includes maintaining a large volume of the compound at a substantially uniform viscosity by recirculating the compound through a conduit system by means of a positive displacement pump, adjusting the resistance to flow of said compound by throttling the flow of said compound in said conduit system to vary the work performed on said compound and thereby to secure the release of the heat equivalent of the work performed on the compound as sensible heat within the compound in such amount and at such a rate that the compound being circulated is maintained at a substantially uniform temperature, intermittently discharging a minor fraction only of said circulating compound at a substantially uniform rate onto successlve container closures and continuously maintaining the volume of the compound being circulated by entraining the makeup quantity of the compound in the low pressure side of the circulating stream at a point approaching the inlet side of the pump. I

5. The process of lining container closures with controlled uniform amounts of a heated, paste- 7 type lining compound which is characterized by a large change in viscosity with a small change in temperature, which includes maintaining a large volume of the compound at a substantially uniform viscosity by recirculating the compound through a conduit system by means of a positive displacement pump, intermittently discharging a minor fraction only of said circulating compound at a substantially uniform rate onto successive container closures from a predetermined discharge point in said system, regulating the resistance to flow of said compound by throttling the flow of compound in said conduit system ata point beyond said discharge point to regulate the amount of work done on the compound and to secure the release of the heat equivalent of the work performed on the compound as sensible heat within the compound in such amount and at such. a rate that the compound being circulated is maintained at a substantially uniform temperature and continuously supplying fresh compound to said system at a makeup point beyond said throttling point, said circulating pump positioned in said system at a point between the point of makeup and the point of discharge.

HENRY E. COOPER.

DUN'BAR L. SHANKLIN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 328,714 Ralston Oct. 20, 1885 1,942,383 Dickhaut Jan. 2, 1934 1,993,973 McNeil Mar. 12, 1935 2,256,777 Kaulen Sept. 23, 1941 

1. THE PROCESS OF LINING CONTAINER CLOSURE WITH CONTROLLED UNIFORM AMOUNTS OF A HEATED, PASTE-TYPE LINING COMPOUND, WHICH IS CHARACTERIZED BY A LARGE CHANGE IN VISCOSITY WITH A SMALL CHANGE IN TEMPERATURE, WHICH INCLUDES MAINTAINING A LARGE VOLUME OF THE COMPOUND AT A SUBSTANTIALLY UNIFORM VISCOSITY BY RECIRCULATING THE COMPOUND THROUGH A CONDUIT SYSTEM BY MEANS OF A POSITIVE DISPLACEMENT PUMP, ADJUSTING THE SPEED AND THE DELIVERY PRESSURE OF THE PUMP TO SECURE THE RELEASE OF THE HEAT EQUIVALENT OF THE WORK PERFORMED ON THE COMPOUND AS SENSIBLE HEAT WITHIN THE COMPOUND IN SUCH AMOUNT AND AT SUCH A RATE THAT THE COMPOUND BEING CIRCULATED IS MAINTAINED AT A SUBSTANTIALLY UNIFORM ELEVATED TEMPERATURE, INTERMITTENYLY DISCHARGING A MINOR FRACTION ONLY OF SAID CIRCULATING COMPOUND AT A SUBSTANTIALLY UNIFORM RATE 